Paracervical blockade may be used as a means of reducing pain during the first stage of labour. Pain associated with uterine contraction and cervical stretching and dilatation is transmitted from these structures on visceral afferents which accompany sympathetic fibres. These pass sequentially through the uterine, cervical, inferior hypogastric and superior hypogastric plexuses to the lumbar and lower thoracic sympathetic chains. During early labour, the bulk of these enter the spinal cord at the T11 - T12 segments. As pain becomes more severe, the two adjacent segments, T10 and L1 become involved (1) (Figure 46.1).

The block is performed bilaterally with the patient in the lithotomy position. The proximity of the broad ligaments just deep to the lateral fornices of the vagina is exploited with the aim of interrupting pain transmission at the level of the uterine and pelvic plexuses (2) (Figure 46.2). An 18.5 cm needle with a security tip (Iowa trumpet, Kobak) is used to limit the injection to within 1.5 - 2 cm of the epithelium. The needle is connected to a 20 ml Luer-Lok syringe. Measures to avoid intravascular injection are vital. After careful aspiration non-adrenaline containing local anaesthetic solution is infiltrated. The specific injection sites have been variously described: 3 and 9 oclock; 4 and 8 oclock; or alternatively all sites (2, 3). The distribution of radio-opaque dyes observed in X-ray studies is similar (4). An interval of 15 minutes should be observed between injections during which time signs of maternal (Table 36.4) and fetal toxicity should be excluded.

Paracervical blockade can be used to provide analgesia during the first stage of labour when contraindications of epidural analgesia are present (Chapter 2). The optimal time for institution of this block is the accelerated phase of the first stage when the severity of pain increases. The presenting part is typically engaged. The cervix is thin and effaced and has a tendency to be drawn up during uterine contractions (2). Paracervical blockade does not provide analgesia of the perineum during the second stage during which pain is transmitted primarily via the pudendal nerves to the S2 - 4 spinal cord segments (Figure 21.1).

The technique has several limitations. The failure rate is reported to be as high as 18% (5). The proximity of uterine blood vessels in the vaginal fornices creates maternal and fetal risks. Fetal bradycardia occurs in 10-50% of cases (6). This is attributed to asphyxia which is believed to result from transient uterine artery vasospasm due to high concentrations of local anaesthetic in the paracervical region. The technique has a duration of action limited to 90 minutes with plain lignocaine. The use of adrenaline or bupivacaine in an attempt to increase the duration of the block should be avoided as both increase the incidence of fetal bradycardia (2, 3).

References:
1. Bonica JJ: Obstetric Analgesia and Anesthesia World Federation of Societies of Anaesthesiologists Amsterdam 2nd ed. 1980.

2. Kobak AJ, Sadove MS: Combined paracervical and pudendal nerve blocks- a simple form of transvaginal regional anesthesia Am. J. Obst. Gyn. 1961; 81:72

3. Marx G, Bassell G ed ; Obstetric Analgesia and Anesthesia Monographs in Anaesthesiology , vol 7 Excerpta Medica New York, 1980 p233-235.

4. Spanos WJ, Steele JC: Obstet Gynecol 1959; 13: 129.

5. Pitkin PM, Goddard WB: Obstet. Gynecol. 1963;21: 737-744.

6. Cibils LA: Am. J. Obstet. Gynecol. 1976; 126: 202- 210